Metal pad offset for multi-layer metal layout

ABSTRACT

A semiconductor device includes a first layer including a number of first layer metal pads, a second layer formed on top of the first layer, the second layer including a number of second layer metal pads, and vias connecting the first layer metal pads to the second layer metal pads. A surface area overlap between the first layer metal pads and the second layer metal pads is below a defined threshold.

CROSS-REFERENCE

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/866,893 filed on Aug. 16, 2013, the entire disclosure ofwhich is hereby incorporated herein by reference.

BACKGROUND

Many semiconductor devices make use of interconnect layers that connectcircuitry from electronic components formed on one layer to electroniccomponents formed on either a different layer or a different chip to bebonded with the interconnect layer. For example, an image sensor arraymay be bonded to an interconnect layer that connects the individualpixels within the array to addressing circuitry that is formed on adevice wafer and bonded to the interconnect layer. Each layer within themulti-layer interconnect layer may include metal lines and metal pads.The metal pads have a much larger area than the metal lines and may beused for bonding or for via landings.

During the formation of metal pads within the interconnect layer, achemical-mechanical polishing (CMP) process is often used to level outthe top of the metal pads that have been deposited into a substrate. Insome cases, the CMP process causes a dishing effect in the metal pads.As the metal pads from multiple layers are formed over each other, thisdishing effect accumulates. The top layer metal pads may thus have asubstantial dishing affect which may cause difficulties when bonding theinterconnect layer to another wafer such as a carrier wafer. Thus, it isdesirable to find ways of forming interconnect layers with metal padswithout the dishing effects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1A is a diagram showing an illustrative multi-layer metal padlayout, according to one example of principles described herein.

FIG. 1B is a diagram showing an illustrative multi-layer metal padlayout that has been adjusted to reduce dishing effects, according toone example of principles described herein.

FIGS. 2A and 2B are diagrams showing illustrative offsets between metalpads of adjacent layers, according to one example of principlesdescribed herein.

FIGS. 3A and 3B are diagrams showing illustrative top views of metal padoffsets between adjacent layers, according to one example of principlesdescribed herein.

FIG. 4 is a diagram showing multiple metal pads per layer having beenadjusted differently to reduce overlap, according to one example ofprinciples described herein.

FIG. 5 is diagram showing an illustrative computing system for modelinglayouts, according to one example of principles described herein.

FIG. 6 is a flowchart showing an illustrative method for adjusting amulti-layer metal pad layout, according to one example of principlesdescribed herein.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIG. 1A is a diagram showing an illustrative multi-layer metal padlayout, according to the present example, each metal pad 102 in eachlayer 104 is aligned with other pads in the other layers. Additionally,the metal pads 102 may be connected to metal pads from different layersthrough vias 105. A via 105 is a hole formed through a material. Thehole is often filled with a conductive material such as metal in orderto provide an electrical connection between two metal pads. Asillustrated, the dishing effects become more severe for the metal pads102 of the upper layers 104.

When forming a metal pad 102 into a multi-layer interconnect layer 100,a metal material is deposited into a hole that is etched into the firstlayer 104-1. A chemical-mechanical polishing (CMP) process is then usedto smooth out the surface of the first layer 104-1. The first layer104-1 may be made of a semiconductor material or a dielectric material.

For a semiconductor material, the first layer 104-1 may include, amongother things, a silicon wafer. Alternatively or additionally, the firstlayer 104-1 may include another elementary semiconductor, such asgermanium; a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; or an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP. In yet anotheralternative, the first layer 104-1 may also include a dielectric layer,a conducting layer, or combination thereof.

For a dielectric material, the first layer 104-1 may be formed of anon-low-k dielectric material having a k value greater than 3.9, such assilicon oxide (SiO₂), silicon nitride (SiN), or silicon oxynitride(SiON). In an embodiment, the first layer 104-1 is formed of an oxidesuch as un-doped silicate glass (USG), boron-doped silicate glass (BSG),phosphorous-doped silicate glass (BSG), boron-doped phospho-silicateglass (BPSG), or the like. The first layer 104-1 may also be formed of asilicon oxide layer and a silicon nitride layer on the silicon oxidelayer. The first layer 104-1 may alternatively be formed of a low-kdielectric material having a k value less than 3.9, such asfluorine-doped silicon oxide, carbon-doped silicon oxide, porous siliconoxide, porous carbon-doped silicon oxide, organic polymers, or siliconebased polymers. In these embodiments, the first layer 104-1 may beformed using a chemical vapor deposition (CVD) or a physical vapordeposition (PVD) process.

In general, such materials 104-1 are harder than the materials used toform the metal pad 102. For example, the metal pads 102 may be made of amaterial such as copper, which is softer than the semiconductor ordielectric material on which the metal is formed. Thus, the CMP processwill cause a dishing effect in the metal pad 102-1. This dishing effectis typically nominal with respect to metal lines because metal lines aremuch narrower in size. The metal pads 102, however, are much larger insize and are thus more prone to dishing. In other embodiments, the metalpads 104 may include a metal or a metal alloy, such as Al, W, Al alloy,Cu alloy, or W alloy.

When forming the next layer 104-2, an inter-layer dielectric (ILD) layeris deposited on top of the first metal pad 102-1 of the first layer104-1. The ILD layer may include one or more of the above-listeddielectric materials for layer 104-1. This ILD layer will be subject toa small amount of dishing because of the underlying dishing effect ofthe first layer 104-1 metal pad 102-1. Thus, when forming the metal pad104-2 above the underlying metal pad 102-1, the dishing effect becomeseven more significant for the second layer 104-2 metal pad 102-2. Thiscumulative dishing effect continues for the metal pad 102-3 of the thirdlayer 104-3 and the metal pad 102-4 of the fourth layer 104-4. Thus, thetop metal pad 102-4 will be subject to substantial dishing due to thenear complete overlap 113 of the metal pads 102. The top layer 104-4 maybe bonded to another wafer such that the top metal pad 102-4 iselectrically connected to a metal pad on the other wafer. For example, adevice wafer may be bonded to the multi-layer interconnect layer 100. Todo this, a passivation layer 106 may be placed over the top metal layer.This leaves a pocket 108 that may cause problems during the bondingprocess. For example, if there are several pockets 108 within thebonding area, the heat resulting from the bonding process will push thatair out to the side, which may cause wafer warping and other issues.Thus, it is desirable to minimize or eliminate this dishing effect.

FIG. 1B is a diagram showing an illustrative multi-layer metal padlayout 110 that has been adjusted to reduce dishing effects. Accordingto the present example, the cumulative dishing effect is reduced byadjusting the metal pad layout so that the amount of overlap 114 isreduced in comparison to the overlap 113 illustrated in FIG. 1A.Specifically, by reducing the overlap 114, the dishing effect does nottransfer to subsequently formed levels as much. Thus, in this example,the overlap between the first layer metal pad 112-1 only partiallyoverlaps with the metal pad 112-2 of the second layer 104-2.

The degree of overlap is reduced below a determined or definedthreshold. For example, it may be determined by a layout designer thatreducing the overlap of metal pads below 50% is sufficient. The overlapmay be defined in a variety of manners. It may mean that for any givenmetal pad, not more than 50% of the surface area will overlap 114 withan adjacent level. Alternatively, it may mean that for an entire layer,the total surface area of all the metal pads on that layer overlaps withmetal pads from an adjacent layer. Other percentages may be used by thedesigner. For example, the designer may wish to reduce the overlap to20%, 30%, 40%, 60% or any range in between those percentages.

The overlap 114 should not be completely eliminated because there has tobe enough overlap 114 to allow the vias 105 to form a sufficientelectrical connection between two metal pads 112 of adjacent layers. Asmentioned above, a via is typically a hole formed between two layersthat is typically filled in with a conductive material. Thus, the term“via” as used herein, refers to a conductive feature between two metalpads. A sufficient electrical connection is one that allows thecircuitry associated with the connection to operate within desiredparameters. Thus, the overlap 114 may be adjusted to be as small as muchas possible while still allowing room for adequate via connections to bemade. FIGS. 2A and 2B are diagrams showing illustrative offsets betweenmetal pads of adjacent layers. FIG. 2A illustrates an example where theoffset direction for each metal pad 202 is in the same direction. Forexample, for each successive layer, the metal pad is offset in a singledirection. Thus, for a given metal pad 204-2 the via 202 connecting to alower metal pad 204-1 is on the opposite side from the via 206connecting to an upper metal pad 204-3. Although a single via is shownbetween each successive metal pad layer 204, more vias may be used. Forthe sake of reference, this arrangement of offset metal pads can begenerally referred to as a stair-step arrangement. In the presentembodiment, metal pad 204-1 is completely non-aligned with andnon-overlapping, from a top perspective, with metal pad layer 204-3.

FIG. 2B illustrates an example where the offset direction for each metalpad 212 alternates between successive layers. Specifically, all the vias214 are aligned while the metal pads alternate in position. Again,although a single via is shown between each successive metal pad layer212, more vias may be used. For the sake of reference, this arrangementof offset metal pads can be generally referred to as a tree-shapearrangement, with the vias representing a trunk of the tree. In thepresent embodiment, the lowest metal pad in the figure is completelyaligned with and overlapping, from a top perspective, with thesecond-highest metal pad in the figure.

Other examples not explicitly illustrated may also be used in accordancewith principles described herein. For example, the stair-steparrangement can advance in one direction for one or more metal padlayers, and then another direction for the next one or more metal padlayers. In another example, the tree-shape arrangement can include oneor more sequential metal pad layers extending in a first direction, andone or more other sequential metal pad layers extending in a seconddirection. In yet another example, the sequence of metal pad layers canstart in one arrangement, such as the stair-step arrangement, and thenchange to a different arrangement, such as the tree-shape arrangement.

FIGS. 3A and 3B are diagrams of illustrative top views of metal padoffsets between adjacent layers. FIG. 3A illustrates a top view 300 oftwo metal pads 302 and 304 overlapping. In some cases, multiple vias 308may be used to connect one metal pad to another metal pad. In thisexample, the first metal pad 302 of a first layer connects to a secondmetal pad 304 of a second layer. Four vias 308 are positioned within theoverlapping region 306. This pattern may continue through successivelayers that are either offset in the same direction or alternatingdirections.

FIG. 3B is a diagram illustrating four metal pads of different layers,each successive layer being offset in one of four directions.Specifically, the first metal pad 312 of a first layer is connected tothe second metal pad 314 of a second layer. A set of vias 320 are usedto connect the two metal pads 312, 314 in the overlapping region.

Additionally, the second metal pad 314 is connected to a third metal pad316 of a third layer above the second layer. A set of vias 322 connectsthe second metal pad 314 to the third metal pad 316. The third metal pad316 is offset in a direction that is perpendicular to the offsetdirection between the first metal pad 312 and second metal pad 314.

Additionally, the third metal pad 316 is connected to a fourth metal pad318 of a fourth layer above the third layer. A set of vias 324 connectsthe third metal pad 316 to the fourth metal pad 318. The fourth metalpad 318 is offset in a direction that is parallel to the offsetdirection between the first metal pad 312 and second metal pad 314.

Other metal layout schemes may be used to reduce the overlap. Forexample the offset directions may be in a variety of directions and notlimited to a specific set. While FIG. 3B shows some overlap between thefirst metal pad 312 and fourth metal 318, the offsets may be adjusted sothat there is no overlap between metal pads in non-successive layers.The metal layout scheme may depend on a variety of factors that includethe design goals of the circuitry.

FIG. 4 is a cross-sectional diagram of multiple metal pads per layerhaving been adjusted differently to reduce overlap. According to certainillustrative examples, each metal pad in a single layer may be adjustedsimilarly, so that each metal pad is offset in the same direction and bythe same distance. This may be done if the metal pads from multiplelayers are aligned. In other cases, however, each metal pad within aspecific layer may be adjusted differently to achieve the goals ofreducing overlap as much as possible.

FIG. 4 illustrates two metal pads 406-1 and 406-2 in a first layer 402and two metal pads 408-1 and 408-2 of a second layer 404. The firstmetal pad 406-1 of the first layer 402 is offset in a first directionfrom the first metal pad 408-1 of the second layer 404. The second metalpad 406-2 of the first layer 402 is offset in a second direction fromthe second metal pad 408-2 of the second layer 404. The first directionis opposite from the second direction.

Additionally, a passivation layer 410 is formed on top of the secondlayer 404. Another wafer 412, such as a device wafer or a carrier wafer,is then bonded to the passivation layer. A device wafer may be aseparately formed semiconductor layer that includes a variety ofcircuitry formed therein. The circuitry of the device layer may beelectrically connected to the metal pads 408. Because the cumulativedishing effect has been reduced, this bonding process can be done moreefficiently and with fewer adverse effects.

FIG. 5 is diagram showing an illustrative computing system for modelinglayouts. According to certain illustrative examples, the physicalcomputing system 500 includes a memory 502 having modeling software 504and data 506 stored thereon. The physical computing system 500 alsoincludes a processor 508 and a user interface 510.

There are many types of memory available. Some types of memory, such assolid state drives, are designed for storage. These types of memorytypically have large storage volume but relatively slow performance.Other types of memory, such as those used for Random Access Memory(RAM), are optimized for speed and are often referred to as “workingmemory.” The various forms of memory may store information in the formof software 504 and data 506. Specifically, the memory may storesoftware for adjusting a multi-layer design layout so that there is lessoverlap between metal pads of different layers.

The physical computing system 500 also includes a processor 508 forexecuting the software 504 and using or updating the data 506 stored inmemory 502. In addition to storing the modeling software 504, the memory502 may store an operating system. An operating system allows otherapplications to interact properly with the hardware of the physicalcomputing system. The processor may, for example, process a set ofcomputer readable instructions that cause the processor to makeadjustments to the circuit design layout to reduce overlap of metalpads.

The layout software 504 may include the tools to extract a multi-layermetal layout from a circuit design. The layout software 504 may alsoinclude the tools to adjust that layout in order to reduce the overlapbetween metal pads of different layers and thereby reduce the cumulativedishing effect.

A user interface 510 may provide a means for a user 512 to interact withthe system. The user may use various tools such as a keyboard or a mouseto input information into the physical computing system. For example,the user 512 may interact with the system to enter design relatedinformation. The user 512 may also specify thresholds for reducing theoverlap. Additionally, various output devices such as a monitor may beused to provide information to the user 512. The output devices maydisplay the circuit design schematics and the adjustments being made.

FIG. 6 is a flowchart showing an illustrative method 600 for adjusting amulti-layer metal pad layout. According to certain illustrative examplesa method for forming a multi-layer metal layout includes a step forextracting 602 a metal layout from a circuit design. For example, acircuit schematic may be designed to perform a particular function. Thiscircuit schematic may be extracted to form the metal layout that willcreate that circuit. This may be done automatically or manually. Thismetal layout may include multiple layers, each layer including a numberof metal pads.

The method 600 further includes a step for adjusting 604 the layout sothat the overlap of metal pads between adjacent layers is reduced belowa defined threshold while leaving enough overlap to form vias betweenmetal pads of adjacent layers. For example, the layout may be adjustedso that the overlap is reduced below a defined threshold. Specifically,a designer may define a threshold of 50%. Thus, the overlap will beadjusted until there is less than 50% overlap of metal pads betweenadjacent layers. This overlap threshold may be the same for each layer.

Alternatively, different layers may have different defined thresholds.For example, the overlap between a first and second layer may have athreshold of 50%. Additionally, the overlap between the second layer anda third layer may have a 40% threshold. The overlap threshold may beselected while considering the minimum overlap that is used forelectrical connection between adjacent layers through the vias. Theminimum overlap may depend on a variety of factors including the metalpad size, via size, and overall layout scheme. In some examples, thesize of a metal pad may be adjusted, if doing so does not adverselyaffect an electrical connection to that pad.

In the foregoing discussion, by fabricating a device, various processes,such as a film deposition process, a lithography process, an etchingprocess, an ion implantation process, a CMP process, and a cleaningprocess, are performed. In the present embodiments, the film depositionprocess includes depositing a physical vapor deposition (PVD) processsuch as evaporation and DC magnetron sputtering, a plating process suchas electrode-less plating or electroplating, a chemical vapor deposition(CVD) process such as atmospheric pressure CVD (APCVD), a low pressureCVD (LPCVD), a plasma enhanced CVD (PECVD), or a high density plasma CVD(HDP CVD), an ion beam deposition, spin-on coating, a metal-organicdecomposition (MOD), an atomic layer deposition (ALD) process and/orother suitable methods.

The present disclosure provides many different embodiments of asemiconductor device and a method for making same. In one embodiment, asemiconductor device includes a first layer including a number of firstlayer metal pads, a second layer formed on top of the first layer, thesecond layer including a number of second layer metal pads, and viasconnecting the first layer metal pads to the second layer metal pads. Asurface area overlap between the first layer metal pads and the secondlayer metal pads is below a defined threshold while still allowing spacefor the vias to make a sufficient electrical connection.

In some embodiments, the lithography process may include coating aresist film on a wafer substrate, exposing the resist film deposited onthe wafer substrate by an optical lithography tool or an electron beamwriter, and developing the exposed resist film to form a resist patternfor an ion implantation process or an etching process. The coating theresist film on the wafer substrate includes performing a dehydrationprocess before applying the resist film on the wafer substrate, whichcan enhance an adhesion of the resist film to the wafer substrate. Thedehydration process may include baking the substrate at a hightemperature for a duration of time, or applying a chemical such ashexamethyldisilizane (HMDS) to the substrate. The coating the resistfilm on the wafer substrate may include a soft bake (SB). The exposingthe resist film deposited on the wafer substrate includes using anoptical exposing tool or a charged particle exposing tool. The opticallithography tool may include an I-line, a deep ultraviolet (DUV), or anextreme ultraviolet (EUV) tool. The charged particle exposing toolincludes an electron beam or an ion beam tool. The using the opticalexposing tool includes using a mask. The mask may be a binary mask(BIM), a super binary mask (SBIM), or a phase shift mask (PSM), whichincludes an alternative phase shift mask (alt. PSM) or an attenuatedphase shift mask (att. PSM). Developing the exposed resist film mayinclude a post exposure bake (PEB), a post develop bake (PDB) process,or a combination thereof.

The etching process may include a dry (plasma) etching, a wet etching,and/or other etching methods. For example, a dry etching process mayimplement an oxygen-containing gas, a fluorine-containing gas (e.g.,CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-containing gas (e.g.,Cl₂, CHCl₃, CCl₄, and/or BCl₃), a bromine-containing gas (e.g., HBrand/or CHBR₃), an iodine-containing gas, other suitable gases and/orplasmas, and/or combinations thereof.

In one embodiment, a method for forming a multi-layer metal layoutincludes extracting a metal layout from a circuit design, the metallayout including multiple layers, each layer including a number of metalpads, and adjusting the layout so that the overlap of metal pads betweenadjacent layers is reduced below a defined threshold while leavingenough overlap to form vias between metal pads of adjacent layers.

In another embodiment, a semiconductor device includes multiple layers,each layer including at least one metal pad, vias providing anelectrical connection between a metal pad of one of the multiple layersto a metal pad of an adjacent one of the multiple layers, a passivationlayer formed on top of the multiple layers, and a carrier wafer bondedto the passivation layer such that electrical connections are made tothe second layer metal pads through the passivation layer. An overlap ofmetal pads between adjacent layers is below a defined threshold whileleaving enough overlap to form vias between metal pads of adjacentlayers.

It is understood that various different combinations of the above-listedembodiments and steps can be used in various sequences or in parallel,and there is no particular step that is critical or required.Additionally, although the term “electrode” is used herein, it will berecognized that the term includes the concept of an “electrode contact.”Furthermore, features illustrated and discussed above with respect tosome embodiments can be combined with features illustrated and discussedabove with respect to other embodiments. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

The foregoing has outlined features of several embodiments. Those ofordinary skill in the art should appreciate that they may readily usethe present disclosure as a basis for designing or modifying otherprocesses and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those of ordinary skill in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device comprising: a first layerincluding a first metal pad; a second layer formed on top of the firstlayer, the second layer including a second metal pad; a third layerformed on top of the second layer, the third layer including a thirdmetal pad, wherein the third metal pad is aligned with the first metalpad, and wherein the third metal pad is not aligned with the secondmetal pad; a first via connecting the first metal pad to the secondmetal pad; a second via connecting the second metal pad to the thirdmetal pad, wherein the second via is aligned with the first via; andwherein, a surface area overlap between the first metal pad and thesecond metal pad is below a defined threshold.
 2. The device of claim 1,further comprising a passivation layer formed over the third layer. 3.The device of claim 2, further comprising a device wafer bonded to thepassivation layer such that electrical connections are made to the thirdmetal pad through the passivation layer.
 4. The device of claim 1,further comprising, additional layers beneath the first layer, theadditional layers comprising additional metal pads, the additional metalpads being offset so that the overlap between metal pads is reduced to adefined threshold.
 5. The device of claim 1, wherein the definedthreshold is within a range of about 40% to about 60% overlap.
 6. Thedevice of claim 1, wherein the defined threshold is about 50%.
 7. Amethod for forming a multi-layer metal layout, the method comprising:extracting a metal layout from a circuit design, the metal layoutincluding multiple layers, each layer including a number of metal pads,wherein the metal layer includes a first layer having a first metal pad,a second layer disposed over the first layer and having a second metalpad, a third metal layer disposed over the second layer and having athird metal pad, wherein the metal layer further includes a first viaextending from the first metal pad to the second metal pad and a secondvia extending from the second metal pad to the third metal pad;adjusting the layout so that the overlap of metal pads between adjacentlayers is reduced below a defined threshold while leaving enough overlapto form vias between metal pads of adjacent layers, wherein adjustingthe layout includes: aligning the first and third metal pads withrespect to each other, wherein the second metal pad is not aligned withrespect to the first and third metal pads after the aligning of thefirst and third metal pads, and aligning the first and second vias withrespect to each other.
 8. The method of claim 7, further comprising,adjusting the layout so that the defined threshold is within a range ofabout 40% to about 60% overlap.
 9. The method of claim 7, furthercomprising, determining an overlap threshold based on at least one of: asize of the metal pads, a size of the vias, and a layout scheme of thelayout.
 10. The method of claim 7, further comprising, adjusting a sizeof one of the metal pads.
 11. The device of claim 1, further comprisinga fourth layer formed on top of the third layer, the fourth layerincluding a fourth metal pad, wherein the fourth metal pad is alignedwith the second metal pad, and wherein the fourth metal pad is notaligned with the third metal pad.
 12. A device comprising: a first metalpad disposed over a semiconductor substrate; a second metal pad disposedover the first metal pad; a third metal pad disposed over the secondmetal pad wherein the third metal pad is aligned with the first metalpad, and wherein the third metal pad is not aligned with the secondmetal pad; a fourth metal pad disposed over the third metal pad, whereinthe fourth metal pad is aligned with the second metal pad, and whereinthe fourth metal pad is not aligned with the third metal pad; a firstvia extending from the first metal pad to the second metal pad; and asecond via extending from the second metal pad to the third metal pad,wherein the second via is aligned with the first via.
 13. The device ofclaim 12, wherein the first metal pad has a sidewall surface that issubstantially coplanar with a sidewall surface of the third metal pad.14. The device of claim 13, wherein the first metal pad has anothersidewall surface that is substantially coplanar with another sidewallsurface of the third metal pad.
 15. The device of claim 13, wherein thesecond metal pad has a sidewall surface that is substantially coplanarwith a sidewall surface of the fourth metal pad.
 16. The device of claim15, wherein the second metal pad has another sidewall surface that issubstantially coplanar with another sidewall surface of the fourth metalpad.
 17. The device of claim 12, further comprising a third viaextending from the third metal pad to the third metal pad, wherein thethird via is aligned with the second via.
 18. The device of claim 12,wherein the first metal pad has a top surface having a total surfacearea, wherein the second metal pad does not overlap more than 50% of thetotal surface area of the top surface of the first metal pad.
 19. Thedevice of claim 18, wherein the third metal pad completely overlaps thetotal surface area of the first metal pad.
 20. The device of claim 12,wherein the third metal pad has a top surface having a total surfacearea, wherein the fourth metal pad does not overlap more than 50% of thetotal surface area of the top surface of the third metal pad.
 21. Thedevice of claim 20, wherein the fourth metal pad completely overlaps thesecond metal pad.